1. Field of the Invention
The invention pertains to the field of mechanical power transmission chains. More particularly, the invention pertains to a limited articulation chain and method for preventing or reducing chain jumping.
2. Description of Related Art
The present invention generally relates to mechanical power transmission chains. A conventional chain drive system includes an endless chain, comprising a sequence of links interconnected by pins, operatively engaged with at least two sprocket wheels supported by shafts. The chain is typically designed such that each consecutive link fits over a xe2x80x9csprocket,xe2x80x9d or what is more commonly referred to as a xe2x80x9ctoothxe2x80x9d of a sprocket wheel. The distance between the links in the chain is known as the xe2x80x9cpitch.xe2x80x9d Typically, mechanical energy from an engine or other power source is applied to the shaft of a driving sprocket wheel, and conveyed by means of the endless chain to a driven sprocket wheel for driving a mechanism. The relative speed of the sprocket wheels varies according to their relative circumferences and, thus, the number of sprockets or teeth on each wheel.
Such mechanical chain drive systems commonly are used in bicycles, motorcycles, conveyor belts, automobiles and various other industrial applications. In a typical engine timing drive application, the driving sprocket is mounted on the engine crankshaft and the driven sprocket is mounted on the camshaft.
There are several types of chain used for the transmission of power. The present invention is applicable to all types of chains, and has particular application to xe2x80x9csilentxe2x80x9d chains, inverted-tooth chains and roller chains, which are well known in the art and widely used in automotive engine timing applications, as well as other automotive applications, such as, for example, in the transfer of power from a torque converter to a transmission or in a transfer case of a four-wheel drive vehicle.
One common type of chain used for the transmission of power is the roller chain. Conventional roller chains typically comprise a sequence of alternate inner links and outer links, wherein the links are interconnected by pins. The inner links, which are also known as bushing links, typically consist of spaced apart inner plates with bushings tightly received in apertures at each end of the inner plates. The outer links, which are also known as pin links or guide links, typically consist of spaced apart outer plates with pins tightly received in apertures at each end of the outer plates. The bushings freely rotate about the pins to pivotally connect the outer links to the inner links in alternate arrangement. Rollers typically are provided on the bushings, and the roller chain is wrapped about a sprocket. The teeth of the sprocket are received between the laterally spaced plates and the longitudinally spaced rollers.
The term xe2x80x9croller chainxe2x80x9d includes both true roller and rollerless designs. The true roller design includes the above-described rollers mounted about the bushings. Rollerless chain or bushing chain contains bushings that directly contact the sprocket. Both types of roller chain are typically specified in industry as British Standard chain and American National Standards Institute (ANSI) chain.
An inverted-tooth chain is similar to a roller chain, but has links made of toothed metal plates. A number of these links are placed side by side to form a group, and each group is joined to the next by meshing the ends of the links of both groups and inserting a pin. The width of an inverted-tooth chain varies with the number of links in each group. A xe2x80x9csilent chainxe2x80x9d is a type of inverted-tooth chain that has been modified to decrease the noise generated during use of the chain.
In many chain drive applications, the links of the chain extend with use and the chain increases in length, particularly during the period of initial use when components of the chain are worn in, or after a long period of service, when components of the chain have worn out. Due to the increased length of the chain, or for other reasons, such as maladjustment, a chain may become slack with respect to its sprockets. One problem with slack in a chain is that it can cause the chain to xe2x80x9cjumpxe2x80x9d or xe2x80x9cskipxe2x80x9d one or more teeth on a sprocket. Particularly in certain applications, such as engine timing, tooth jumping is a significant problem because it negatively affects mechanical performance by altering engine timing, for example.
Thus, there is a need in the art for a chain design that prevents or reduces chain jumping at a given amount of available chain slack. A chain design that prevents or reduces chain jumping is useful for at least two reasons: 1) such a chain design eliminates the need for the ratchet mechanisms that often are added to chain tensioners, in attempts to limit chain slack and reduce tooth jumping; and 2) such a chain design allows small pitch chains, which often are useful in reducing mechanical noise, to be used in applications that otherwise would typically require larger pitch chains.
Briefly stated, a limited articulation chain design that prevents or reduces chain jumping at a given amount of chain slack comprises a chain having a plurality of alternating inner and outer links having ends interconnected by pins, wherein the ends of the outer links are partially or substantially squared on the sprocket side, such that the ends of adjacent outer links limit articulation of the links around the pins to a predetermined radius, by interfering with the adjacent outer links at the predetermined radius.
According to one embodiment, a limited articulation chain design that prevents or reduces chain jumping at a given amount of chain slack comprises a chain having a plurality of alternating inner and outer links, each link comprising a pair of opposed link plates, each link plate having at least two connection apertures located substantially towards the ends thereof, and each link being connected to an adjacent link by a pin passing through overlapping connection apertures in adjacent link plates, wherein the ends of the outer link plates are partially or substantially squared on the sprocket side, such that the ends of adjacent outer link plates limit articulation of the links around the pins to a predetermined radius, by interfering with the adjacent outer link plates at the predetermined radius.
According to another embodiment, a method for preventing or reducing chain jumping at a given amount of chain slack comprises the step of providing a chain drive system with a chain having a plurality of alternating inner and outer links having ends interconnected by pins, wherein the ends of the outer links are partially or substantially squared on the sprocket side, such that the ends of adjacent outer links limit articulation of the links around the pins to a predetermined radius, by interfering with the adjacent outer links at the predetermined radius, such that the chain has a radius of curvature slightly smaller than that of the smallest sprocket in the system.
For a better understanding of these and other aspects of the invention, reference should be made to the following detailed description taken in conjunction with the accompanying figures.